This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. An efficient computational algorithm is necessary to simulate and fit time-domain signals and the respective dipolar spectra provided by the 6-pulse sequence of DQC ESR. The challenge here is to develop an efficient computational algorithm that would not result in astronomic computation time when multiple parameters such as distances and their distributions, nitroxide orientations etc. are simultaneously varied. Also, time domain computations need to be rigorous, as opposed to the existing computational approach based on analytic approximations, which is very fast but inaccurate for distances under 15 [unreadable] for experimentally relevant pulse parameters. We developed a computational strategy that can account for multiple varied parameters and that would still result in acceptable computational time. The time domain computations are based on rigorous density matrix theory and account for dipole-dipole interaction during the pulses. The first milestone of this work is to provide a reliable and efficient computation of the time-domain 6-pulse DQC signal for rigid nitroxide biradicals at experimentally relevant conditions. The second milestone is to account for multiple varying parameters by efficient computation of the starting vector and the reuse of the outcome of the previous iteration step.